What Is a Good Battery Management System for LiFePo4 Battery Pack

A decent BMS should provide adequate protection and have the desired functions. For LiFePO4 batteries, a BMS, or battery management system, is required.

All lithium battery cells, including LiFePO4 batteries, are vulnerable to overvoltage, undervoltage, and overcurrent. A LiFePO4 battery can quickly experience capacity loss, battery damage, or even the risk of fire if one of the aforementioned circumstances is maintained for an extended period of time.

Therefore, the BMS’s main responsibility is to safeguard the LiFePO4 battery cells. They might then be operating at the proper temperature, current, and voltage. It would also be wonderful if additional necessary functions could be accomplished in addition to this.

Basic Purpose and Battery Management System Operation Principle

The most fundamental function of battery management system is to make the battery cells invulnerable, which is also its main duty. PCB, or Protection Circuit Board, is another name for a battery management system with just this one fundamental function. Here are some specific protective guidelines.

Over-Voltage Defense

Over-Voltage Protection for Cells

3.65V cell overvoltage, 3.55V release voltage, and a 2S delay. Each cell’s voltage rises as it is being charged. The charge circuit is cut off when one of the batteries surpasses the 3.65V voltage limit, activating the cell over-voltage protection. During the charge circuit is reconnected, the voltage either discharges naturally to 3.55V or discharges after a 2 seconds delay.

If possible, I personally advise raising the overvoltage protection threshold to 3.60V to prevent the battery from fully charging. Due to the lithium ions building up on the positive terminal, 100 percent SOC is not the most stable state.

Over-Voltage Protection Pack

The next applies to a battery pack with four series-connected 12.8V cells. 14.60V is the pack’s overvoltage limit. 14.20V release voltage with a 2S delay. When the total voltage reaches 14.60V, the charge circuit is cut off, just like with cell overvoltage. The voltage reduces to 14.20V naturally, or when the battery is discharged, and then, after a 2S wait, the charging circuit is restarted.

Hardware Over- Voltage Protection

3.9V, 2S delay hardware overvoltage protection. The battery pack’s final line of defense is hardware protection.

Under-Voltage Protection

Under- Voltage Protection for Cells

Release voltage 2.7V, 2S delay, single-cell under-voltage limit 2.5V. The voltages of the cells are continuously decreasing as they discharge. The discharge circuit will be closed off when one of the cells achieves a voltage of 2.50V. The cell voltage rebounds to above 2.7V after charging or when the voltage naturally rises, and the discharge circuit recover after 2S.

Under- Voltage Protection for Packs

Release voltage 10.80V, delay 2S, and pack under-voltage limit 10V similar steps as before.

Protection against Hardware Under- Voltage

It has 2.0V and 16S.

Over Current Protection

Software (1st grade) Current Defense

Charge over current delay of 10 seconds, release time of 30 seconds, and charge over current of 0.5C (50A if 12.8V100Ah LiFePO4 Battery). The charge circuit will be turned off if the charging current reaches 50A. Discharge over current delay of 10 seconds, release time of 30 seconds, and 1C (100A if 12.8V100Ah LiFePO4 Battery).

Hardware (2nd grade)

Each battery model and battery management system will have a distinct current protection limit of 200A, with a 160mS protection delay.

Protection against Short-Circuits (3rd grade)

It is 1000 A and 40 s. Every battery management system electronic component has a maximum withstand current in general. Most of the battery management system will malfunction if the current reaches 2600A.Main Components of BMS

MCU – The Human Brain

The MCU gathers a variety of data and transmits directives. for instance, temperature, current, voltage, etc. and instruct the relevant MOSFET to open or close the circuit with a command.

MOSFET

Control the circuit’s activation or deactivation. Important factors are withstand voltage and current.

Sensor for Current

To measure current, a current sensor is used. Other small resistors, semiconductors, etc. are available.

Protection from Temperature

A NTC temperature sensor is a necessary component. The MCU uses the temperature value received from the temperature sensor to switch on or off the associated MOSFET.

75°C is what is meant by charge high-temperature protection. Release 55 °C; wait 2 s.

Charge low-temperature protection entails a 0°C, 5°C, and 2S delay.

High-temperature discharge protection is 75°C, Release 55°C, and 2S of delay.

The terms “discharge low-temperature protection” refer to -10°C, release °C, and 2S of delay.

Smart BMS-Cell Balancing

Cell balancing’s primary goal is to maintain each cell in a constant, comparable state for an extended period of time in order to increase the battery pack’s longevity. Active cell balance and passive cell balance are different types of cell balancing.

The active balancing circuit is extremely intricate. Since there are no integration chips, the components are still somewhat huge. The benefit is that the balancing current can approach 10A current and that it doesnt warm up.

A heating resistor is mostly used in passive balancing to eat up the high-voltage cell’s energy. The drawback is that it will heat, and the balancing current—only a few hundred mA—is minuscule. However, passive balancing only needs a little amount of room. Passive balancing has until now made up the majority of the balance module built into BMS.

Communication Module

The communication module enables the battery management system to interact with the outside world, provide data, and modify the internal battery parameters using third-party apps or software. RS232, RS485, CAN, UART, and other common communication module interfaces are listed below. These ports enable direct communication between the battery and the inverter and allow the inverter or the entire smart system to receive data directly from the battery. Alternatively, you can use your computer’s USB port to read the battery statistics, change parameters, and do other things.

Bluetooth Module

The communication module is actually the foundation for the Bluetooth function. To achieve the goal of Bluetooth communication, the port of the communication module UART or RS232 connects with the Bluetooth module.

In addition to reviewing SOC, remaining energy, voltage, current, individual cell voltages, and other data, a capable Bluetooth app is able to do much more. To personalize the battery specifically yours, you can also change the battery management system protection parameters as you choose.

Bluetooth monitor

Electronic Switch

The discharge circuit can be switched on and off electronically.

Self-heating module

The battery’s interior can be warmed up by the self-heating module during the outside temperature falls below 0°C and the charge current starts. The charge current may still be able to charge the battery once the temperature rises over 5 °C. The battery is actually being able to be charged at a 5°C in this situation.

GPS module

The battery may be located using the satellite positioning system with the help of the integrated GPS module, allowing for the management of all battery locations and operational status across a network.

The Most Important Function A Battery Management System Performs

The most crucial task a battery management system completes is cell protection. A battery management system is necessary to provide overvoltage protection since lithium ion battery cells have two serious design flaws that can lead to damage, overheating, explosions, or flames.

Lithium ion batteries can also sustain damage if their discharge falls below a predetermined cutoff point, which is roughly 5% of their full capacity. The cells’ capacity may be permanently lowered if the discharge falls below this level.

A specialized Lithium-ion protector is a safeguard feature of a battery management system that makes sure a battery’s charge doesn’t go above or below its limitations. Every battery protection circuit has two “MOSFETs,” which are electronic switches. MOSFETs are semiconductors that are utilized in circuits to turn on and off electrical signals.

A discharge MOSFET and a charge MOSFET are often found in battery management systems. The charge will be stopped by opening the Charge MOSFET chip if the protector determines that the voltage across the cells is greater than a predetermined threshold. The switch will shut off once the charge has returned to a secure level. Similar to this, the protector will stop the discharge when a cell drains to a particular voltage by opening the Discharge MOSFET. 

Energy Management

The power meter on your laptop battery is a fantastic illustration of energy management. Today’s laptops can typically inform you how much battery life is still remaining, as well as your rate of consumption and how long you have left before the battery needs to be recharged. Energy management is therefore crucial for portable electronic devices in practice.

A “Coulomb counting” is the secret to effective energy management. For instance, if there are five people in a room and two leave, there are now three left, and if three more people join, there are now six individuals in the space. If the room can accommodate 10 individuals and only 6 are present, it is 60% filled. A battery management system monitors the capacity. When you click a button on a state of charge display, an LED display provides you a reading of the total charge in increments of 20 percent, which is how the user is informed electronically of this state of charge.

For specific applications, such as the one for this portable point-of-sale terminal, battery management systems also comprise an integrated charger made up of a control device, an energy storage device called an inductor, and a discharger. The charging algorithm is controlled by the control device. The ideal charging procedure of lithium-ion batteries is to use constant voltage and constant current.

A battery pack typically comprises of a number of separate cells that cooperate. A battery pack’s cells should ideally be maintained at the same level of charge. Individual cells may get stressed if the cells are out of balance, which can result in an early termination of the charge cycle and a reduction in the battery’s total cycle life. The battery’s lifespan is increased by the cell balancers of the battery management system, which are seen here. They stop this imbalance of charge in individual cells from happening.

Conclusion

Lifepo4 batteries are made up of many cells that are joined together. Additionally, it has a Battery Management System (BMS) that controls each battery cell to keep it within safe limits but is invisible to the end user. battery management system extends lifespan, monitors, balances, and communicates with various modules to ensure safe operation under a variety of circumstances.

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